This invention relates to a cooling system for a vehicle.
It is known to provide a vehicle having an internal combustion engine with a cooling system which includes a high temperature cooling circuit and a low temperature cooling circuit separated from the high temperature cooling circuit. The engine is cooled by a high temperature cooling circuit. The low temperature cooling circuit cools an oil cooler and, if necessary, a charge air cooler.
Such a known system is described in DE 41 14 704 A1. In this cooling system the engine has a charge air cooler and is cooled in the high temperature cooling circuit by means of the high temperature re-cooler. The coolant temperature in the high temperature cooling circuit is approximately 90 to 110° C. In the low temperature cooling circuit, which is separate from the high temperature cooling circuit, the charge air cooler, an engine oil cooler and a gearbox oil cooler are cooled by the low temperature re-cooler. The temperature of the coolant in the low temperature cooling circuit is approximately 45 to 90° C. The high temperature re-cooler and the low temperature re-cooler are both air-to-coolant heat exchangers and are referred to below as a cooler for the sake of simplicity.
With the cooling system of DE 41 14 704 A1, the charge air cooler is cooled by both cooling circuits. This cooling system includes an embodiment wherein the gearbox oil cooler is cooled along with the coolant from the high temperature cooling circuit together with the coolant from the low temperature cooling circuit in order to be able to remove large amounts of heat.
However, it is difficult for this known cooling system to directly and rapidly react to the momentary loads of the vehicle. While control valves are provided in the two cooling circuits for conducting the coolant past the individual coolers, nevertheless this cooling system cannot quickly react to sudden changes in the engine load quickly, and it cannot maintain an essentially constant oil temperature.